Today, most legal recreational marijuana operations are small, limited to a single state and barred from ever getting large by regulators who want to keep a close eye on the fast-growing industry. But those small operators struggle to get bank loans for expansion, often produce an inconsistent product and sometimes have no idea how to balance supply and demand for their crops.

And many fear that tobacco companies, with their deep pockets, longstanding experience dealing with heavy government regulation, and relationships with generations of farmers will jump into the burgeoning marijuana market. At marijuana business conventions and in private conversations, it sometimes seems like everyone has heard a rumor about Big Tobacco getting in.